1. Field of the Invention
The present invention relates to an apparatus and a method for switching an operation mode of a high definition television system for receiving both terrestrial broadcasting signals and cable broadcasting signals. More particularly it relates to an apparatus and a method for switching the operation mode of the high definition television (hereinafter referred to as HDTV) system which uses Vestigial Side Band (VSB) modulation.
2. Description of the Related Art
Ever since the Federal Communication Committee (FCC) adopted a broadcasting standard for black and white TV in 1941; color TV, an enhanced definition TV (EDTV) and an HDTV, which has been called the next generation TV, have been sequentially developed. The development of such TV systems are the result of the desire of people who wish to enjoy, through TV, more realistic scenes which look like the real scene.
In contrast to technological developments in electronics, communications, etc., which have changed rapidly, the lifetime of the presently used TV broadcasting standard has been very long, because it is difficult to change the broadcasting standard.
The conventional color TV, which is widely used, operates based on several broadcasting standards: National Television System Committee (NTSC) which is used in Korea, the United States, Japan, etc.; phase alternation by lines (PAL) used in Europe; and sequential color memories (SECAM). However, the standard specifications have been decided based upon the black and white TV technology of 1940, and that technology has been used up until now.
An improved definition TV (IDTV) standard which appeared prior to HDTV, provides a clearer picture to the viewer by enhancing the receiver function of the conventional color TV. The IDTV standard converts the interlaced scanning method of the conventional color TV into a progressive scanning method, and adds display functions and removes "ghosts".
Based upon the conventional color TV broadcasting standard, EDTV enhances presentation performance by enlarging the aspect ratio to 9:16, as in a movie. However, both the IDTV and EDTV standards do not exceed the limits of the conventional TV broadcasting standard. Accordingly, many trials have been held to ensure that a picture results which is clearer than the conventional color TV picture, and the HDTV standard appeared to be in compliance with these trials.
The `HDTV` standard is defined by International Telecommunication Union-RS (ITU-RS) as follows: a TV which has a vertical/horizontal resolution more than two times that of the conventional TV; solves the problems which occur in conventional TV, such as a cross color; has an aspect ratio of 9:16,wider than the conventional TV; and has an associated digital audio performance which is the same as compact disk (CD) quality. As noted in the ITU-RS definition, HDTV, in short, provides a clearer picture and higher audio quality.
The HDTV systems developed up until now are categorized as two types of systems, according to signal transmission method. The first one is a sampled value transmission system for transmitting a digital signal as an analog signal. It is applicable to a multiple sub-Nyquist sampling encoding (MUSE) system used in Japan and a high definition-multiplex analogue component (HD-MAC) system used in Europe.
The other one is a full-digital system which digitally processes and transmits the signals, and is now actually being used in the United States.
More specifically, the full-digital system increases the number of channels in the conventional broadcasting system (i.e., the number of programs capable of being broadcast) by four to ten times at the 6MHz bandwidth occupied by the conventional broadcasting signals. In the United States, by applying the technology already developed for HDTV broadcasting, cable television (CATV) broadcasting having 540 channels and satellite broadcasting having 150 channels has begun. The application of the full-digital system is not limited to broadcasting, but its applicability extends to the computer and communication fields.
The development of the full-digital system started when the FCC-adopted system for the next generation of TV, namely advanced TV (ATV), was launched at 1987. The ATV system transmits the HDTV signal by means of a 6 MHz signal which is the transmission bandwidth occupied by one terrestrial broadcasting channel. The HDTV signal is compressed into a bandwidth of 6 MHz by using image compression techniques. Since it is impossible to send the HDTV signal at about 1.2 Gbps through a current channel, the signal can be transmitted after the bandwidth of the input signal is compressed in compliance with the bandwidth of the channel. For this purpose, a bit rate reduction by a factor of 50 or higher is required.
The FCC family excluded the analog MUSE system proposed by NHK of Japan in the standardization operation phase in which many research organizations and companies participated. Accordingly, the companies competing with each other finally formed three consortiums and all three consortiums have adopted the full-digital system, and this system has become the standard for the United States.
One of these three consortiums is comprised of Massachusetts Institute of Technology (MIT) and General Instrument (GI), which proposed a channel-compatible digichiper HDTV system. American Telecommunication & Telegram (AT&T) and Zenith comprise another consortium which proposed a digital spectrum compatible HDTV system. The third consortium which is the Advanced Television Research Consortium (ATRC) organized by Philips, Tomson, David Sarnoff, NBC and CLI, proposed an ADTV system. In order to ensure the most proper characteristic and compatibility between the competitive systems, the Grand Alliance (GA) was is established.
The Grand Alliance HDTV (GA HDTV) system has tried to strike a balance in order to satisfy the requirements for simultaneous broadcasting of HDTV, which is the capability of maintaining compatibility with the conventional color TV standard, i.e., the NTSC standard.
The GA HDTV system adopts the data compression method based upon both Motion Picture Experts Group-2 (MPEG-2) and 8-VSB (Vestigial Side Band) for the channel coding method for terrestrial broadcasting. Moreover, it is convincing that 16-VSB channel coding method can be adopted for use in cable broadcasting.